A wide variety of mechanical heart valve prostheses have been developed to operate hemodynamically, in conjunction with the pumping action of the heart, which are designed to take the place of defective or diseased natural valves. These valves typically have valve bodies which accommodate valve members either in the form of a single occluder or in the form of multiple occluders or leaflets, which valve members generally pivot along eccentric axes to open and close a central blood flow passageway through the valve body. Alternatively, some mechanical valves utilize valve members that both pivot and translate to open and close such a central blood flow passageway.
In its open position, a prosthetic heart valve desirably provides a central blood flow passageway which is large and which has good flow characteristics so that blood flows freely therethrough without adverse boundary layer separation and with a minimum of drag. A heart valve mounted in the aortic position should be very responsive to blood flow so as to open quickly during the pumping stroke of the heart and to close quickly when the associated chamber of the heart relaxes so as to prevent substantial regurgitation of the blood. The opening and closing of the valve should also be sufficiently soft so that the patient is not disturbed by the sounds produced and so that impacts on the valve body are minimal. The heart valve must be made of materials that are biocompatible and thromboresistant, and in this regard, it is important that all surfaces be well washed by blood to prevent regions of stagnation which might lead to eventual clotting. Furthermore, the action of the valve should be such that it does not cause hemolysis (damaging of blood cells), and of course, the heart valve should be constructed to withstand countless openings and closures without the valve members jamming or escaping.
Prior art multi-leaflet heart valves have offered a variety of designs and configurations intended to address the some of the aforementioned problems. For example, U.S. Pat. No. 4,272,854 (Jun. 16, 1981) shows an early version of a bileaflet heart valve having an ear extending from each lateral side of each leaflet, which ear pivots in a recess, guided in part by a knob traveling in a longitudinal slot that is cut more deeply into the sidewall of the valve body.
U.S. Pat. No. 4,363,142 (Dec. 14, 1982) discloses a bileaflet heart valve wherein the leaflets have laterally extending ears in the form of generally oval or spherical projections that are received in recesses of complementary design.
U.S. Pat. No. 4,373,216 (Feb. 15, 1983) discloses a bileaflet heart valve wherein protrusions, extending generally radially inward from a pair of flat sidewall sections of the valve body, guide valve members which have slots in their lateral edges which fit about such protrusions. U.S. Pat. No. 4,451,937, (Jun. 5, 1984) shows a generally similar bileaflet heart valve where the pivot arrangement is formed with a reversal of these parts so that the leaflets have laterally protruding ears which are received within slots in the valve body sidewall that guide the opening and closing movements.
U.S. Pat. No. 4,308,624 (Jan. 5, 1982) discloses heart valves of both the single occluder and bileaflet type having curved valve members which both rotate and translate in moving between the open and closed positions, being guided by laterally extending ears that travel in slots. Later versions of this valve are disclosed in U.S. Pat. No. 4,357,715 wherein an elongated depression within each slot in the valve sidewall controls lateral movement within the slot, and also in U.S. Pat. No 4,443,894 (Apr. 24, 1984) wherein the slots are of kidney bean shape.
U.S. Pat. No 4,808,180 (Feb. 28, 1989) discloses a bileaflet valve wherein the leaflets each have a semi-conical shape and thus inherently provide significant resistance to blood flow through the valve in the open position. The leaflets are guided by generally C-shaped rails that protrude from the valve body sidewall and are received in recesses of complementary shape in the lateral edges of the semi-conical leaflets.
U.S. Pat. No. 5,207,707 (Jan. 16, 1992) discloses a trileaflet heart valve wherein the leaflets translate between open and closed positions guided by ears 74 which travel along curved grooves 40 carved in walls of a pivot structure 26 that are open at their downstream ends. U.S. Pat. Nos. 4,820,299 and 5,123,918 also disclose generally similar trileaflet prosthetic heart valves. The latter illustrates a construction wherein specially configured edge guide arcs are formed in the respective faces of three triangular projections that protrude from the interior surface of the valve body. These arcs extend from the downstream edge of the valve body in a circular section that swings radially inward and then back in a direction toward the interior surface of the valve body, and they guide such leaflets in moving between the open and closed positions.
Commercially developed mechanical heart valves have frequently employed valve members oriented at a significant angle to the valve centerline in the open position, so that when backflow of blood begins, it preferentially impinges strongly upon the outflow surfaces of such valve members. This arrangement initially imparts a strong pivotal force component in the direction of closing movement which contributes to prompt closing and minimal regurgitation. It is now felt that it is particularly important for a mechanical heart valve prosthesis to provide a passageway through which blood can freely flow in the open position with a minimum of drag, and to accomplish this desired objective, it is presently believed that valve members should be able to follow the flow and, when required, assume orientations parallel or nearly parallel to the longitudinal axis of the passageway. Of course, such valves should promptly close with only a small amount of regurgitation and without creating any significant cavitation.
In summary, there is a desire for trileaflet mechanical heart valves which have such improved flow characteristics in the open position, which are reliable and responsive in leaflet movement and which are designed to avoid cavitation and the likelihood of clotting. Trileaflet heart valves which meet these criteria continue to be sought.